On 14/05/2015 17:23, Alex Williamson wrote: > > Would irq_ack_notifiers be used at all with this patch set? Resampling > > of IOAPIC level-triggered interrupts would be implemented in userspace. > > For the same reason, assigned devices using legacy device assignment > > probably would not be able to use INTX (so this feature should depend on > > !KVM_DEVICE_ASSIGNMENT). Add the emulated i8254 and the last user of > > irq_ack_notifiers goes away. > > > > Alex, how does VFIO do INTX resampling if you're using TCG or -machine > > kernel_irqchip=off? (Context: this series keeps the local APIC > > emulation in the kernel, thus including MSI, but moves the IOAPIC > > emualtion to userspace). > > Without KVM irqchip, we use a rudimentary approach where we disable > mmaps to the device when an interrupt occurs. This makes us trap all > accesses to the device. We then handle any device access from the guest > as a potential EOI and unmask the interrupt. If the interrupt re-fires, > we've at least rate-limited it. If it doesn't, a timer eventually > re-enables devices mmaps. It's not very efficient, but it works (for > both PCI and platform devices) and avoids IRQ APIs through QEMU that get > very platform/machine specific. Thanks, If we move the IOAPIC back to userspace, it probably would be easier to implement irqfd/resamplefd in userspace as well. Let the bikeshedding start! Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
